One day near the turn of the millennium, during a short drive, Piotr Kozieradzki played Marillion in his car for Piotr Grudziński. While drummer Piotr 'Mitloff' Kozieradzki had played in two death metal bands, Dominion and Hate, and Piotr Grudziński had played guitar in a metal band, Unnamed, they both shared a deep affection for progressive rock. They were already friends with producer and keyboardist Jacek Melnicki who also owned his own studio. The three decided to experiment with progressive music but they needed a bass player to complete the lineup. Mariusz Duda, multi-instrumentalist and vocalist from the band Xanadu, agreed to attend a rehearsal in late fall of 2001 at the request of Jacek. Reactions to this first meeting between the four experienced instrumentalists were extremely positive.

After a few rehearsals, the members realized that they were involved in something special and deeply satisfying. Once a few compositions were completed, Mariusz attempted to sing in his own language, singing that was probably similar to the vocalizations in their future track "The Curtain Falls", although all future vocals and lyrics were to be written in English. Thus Mariusz began to take on the role of vocalist as well as that of the bass player. In October 2002, about a year after their formation, the band performed a pair of shows in Warsaw. After the distribution of about 500 copies of their demo, the band performed at a small club in Warsaw once again in early 2003. As the band continued to write more material for a full length release, there grew a dissonance between keyboardist Jacek and the other members of Riverside. Jacek wished to continue with his studio pursuits so, during the latter part of 2003, he split from the group.

The rest of the band was left to mix their first album, which was to be entitled Out of Myself. It was released in Poland in late 2003. The success of the album in Poland and the live shows that the band performed led to a release of the album on American record label Laser's Edge in September 2004, this time with cover art from Travis Smith, painter for bands such as Opeth, Anathema, and Devin Townsend. The album Out of Myself has won best debut in many magazines and websites such as Metal Hammer and Belgium Prog-Nose.

Following their 2003 debut Out of Myself and the success that followed in 2004, the band began working on an EP entitled Voices In My Head which was at first a release exclusive to Poland through the label Mystic Production. The quartet from Poland performed their first foreign gig at the Progpower festival in the Dutch city of Baarlo. The band were taken in by major prog label InsideOut, releasing Second Life Syndrome in late October 2005. The album was a massive success, expanding the scope of the band's reach even further than Out of Myself. The album holds a formidable spot as number 62 on Prog Archives top 100 prog albums as well as the number one rated album of 2005.[1] In 2006, Voices In My Head, the EP originally released in Poland only, was re-released under the InsideOut label, now revamped with the inclusion of three high quality live tracks off the Out of Myself album. In addition, the band played their first overseas show at NEARfest in Bethlehem, Pennsylvania on 24 June 2006. Soon after, the band would begin writing for its third full length album and final instalment in the Reality Dream Series.

In October 2007, the band released the album Rapid Eye Movement, once again under the InsideOut label. The European release had the standard nine tracks but the American release saw two versions of the album. One was a single CD with the nine tracks from the album, plus three tracks from their 02 Panic Room Single. This single was also exclusive to Mystic Production and therefore mostly unavailable to oversea fans. The other version contained 2 CDs, the first with the nine album tracks and the second disc containing the three songs from the single as well as two new, more atmospheric, compositions. Before the release, the band toured in support for Dream Theater on the European leg of their tour, exposing them to even more potential fans. Mariusz Duda recently released the debut album from his new project, Lunatic Soul. The self-titled album was released by Kscope on 13 October 2008.[2]

The quartet's next album was "Anno Domini High Definition".[3] Mariusz Duda had the following to say about the album on 27 January 2009:

"We have gone from Warsaw, we have changed the studio and the producer. We care deeply about creating a coherent record and that is why most probably there are only going to be five songs on it. The material will be energetic, multifarious, and - I hope so - very good for live performances. It will be a story about liquid modernity, life in a constant hurry, stress and anxiety about the future. A picture of our times in 1920 x 1080 definition."

The record was released in Poland by Mystic Production on 15 June 2009. Anno Domini High Definition became the best selling album in Poland during its second week on the charts, following a debut at sixth place.:[4] The album was released on 6 June in the rest of Europe and on 28 July in North America. The band has tracked their recording process with the blog and website annodomininihighdefinition.com (Which is now not a registered domain name.).

The Limited Edition of Anno Domini HD is a 2-disc set. The second disc is a DVD that contains a seven-song video production. The show was taped at the Paradiso Theater in Amsterdam.